In 1242, the earl of Leicester, Simon de Montfort, quipped that his brother-in-law and monarch, King Henry III of England, should be locked up like Charles the Simple. Recalling these words, the aphorism ‘ever a true word is spoken in jest’ comes instantly to mind, for some twenty years later, Henry III did become a prisoner, and Simon de Montfort was his jailer. For a period of fifteen months, between the crushing defeat of the royal army at Lewes on 14 May 1264, and Montfort's brutal murder at Evesham on 4 August 1265, Henry III lost control of his seal, his household and his kingdom as he was forced to accept the appointment of new officials at the centre and periphery of government.

This was not the first time in his long reign that Henry lost power over his kingdom. Between June 1258 and January 1261, the king relinquished the great seal to a group of fifteen barons, without whom he could not govern. Between July and October 1263, the seal was taken from the king again. However, on neither occasion were Henry III's authority and physical freedom severely restricted. Between November 1259 and April 1260, Henry circumvented baronial control through his prolonged absence in France to ratify the Treaty of Paris. In 1263, restrictions on royal authority were removed when the king slipped from Montfort's grasp and joined his son and heir at Windsor castle.

Learning from past mistakes, the baronial reformers (Simon de Montfort in particular) made sure that Henry's loss of power between the battles of Lewes and Evesham was near total. From the Ordinance imposed in June 1264, which provided for the governance of the realm by a group of nine councillors, chosen by three electors (Simon de Montfort, the earl of Gloucester Gilbert de Clare and the bishop of Chichester Stephen Berksted), it is apparent that Henry had little control over his kingdom's precocious bureaucracy. The extent of the king's political emasculation can be gleaned from the chancery rolls. To perpetuate the fiction that the new council was fulfilling Henry III's mandate, chancery missives were issued in the king's name throughout his captivity, just as they had been during the period of baronial reform between 1258 and 1260.